Scalable and high yield synthesis of transition metal bis-diazabutadienes

ABSTRACT

The present disclosure is directed at the synthesis of transition metal bis-diazabutadienes as precursors to enable atomic layer deposition (ALD) or chemical vapor deposition (CVD) of transition metals on metallic surfaces. The transition metal bis-diazabutadienes may be prepared in a two-step synthetic procedure at relatively high yields and are particularly suitable for industrial scale-up.

FIELD

The present disclosure is directed at the synthesis of transition metalbis-diazabutadienes as precursors to enable atomic layer deposition(ALD) or chemical vapor deposition (CVD) of transition metals onmetallic surfaces.

BACKGROUND

Transition metal bis-diazabutadienes [(DABD)₂M] have been previouslyidentified as precursors that enable the selective ALD or CVD oftransition metals on metallic surfaces. See, C. Winter et al,Organometallics 2011, 30, 5010-5017. In addition, (DABD)₂M precursorsavoid deposition on adjacent dielectric surfaces such as SiO₂ or lowdielectric constant organic interlayer dielectrics (low-k ILDs). Thisselectivity is a characteristic of the chemical make-up of the (DABD)₂Mprecursors and chemical passivation of the undesired surface may not berequired. However, existing methods of preparation of M-DABD arerelatively low yielding and plagued by the formation of undesiredby-products (Winter et al).

The growth of material layers by ALD generally involves the followingsteps: (1) exposure of the substrate to a first precursor of anorganometallic compound that modifies the substrate surface; (2) purgeor evacuation of the reaction chamber to remove non-reacted precursorsand other gaseous reaction by-products; (3) exposure to a second gaseouschemical composition that reacts with the modified substrate surface toform a film. A purging gas may then be introduced to remove any residualsecond chemical composition and the steps may be repeated.

BRIEF DESCRIPTION

The above-mentioned and other features of this disclosure, and themanner of attaining them, may become more apparent and better understoodby reference to the following description of embodiments describedherein taken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates a reported one-step synthesis of (DABD)₂M complex viathe reaction of DABD, metal chloride and lithium metal intetrahydrofuran (TFH).

FIG. 2 illustrates a two step method for synthesis of a (DABD)₂Mcomplex.

DETAILED DESCRIPTION

The present disclosure is directed at methods of synthesizing, atrelatively high yields, molecular precursors to enable ALD or CVD oftransition metals on metallic surfaces. The molecular precursors fallgenerally in the category of transition metal bis-diazabutadienecomplexes. The transition metals may therefore include transition metalsselected from Groups 3-7 of the periodic table. Preferably, thetransition metal includes Fe, Co, Ni or Cr. The precursors so preparedat relatively high yields may then be conveniently employed in ALD orCVD coating procedures.

FIG. 1 illustrates a reported synthesis of (DABD)₂M via the indicatedone-step reaction of DABD ligand, metal chloride and lithium metal inTHF. See, U.S. Patent Appl. Publ. No 2013/0164456; Winter et al, notedabove. This one-step reaction provides the indicated (DABD)₂M precursorat yields of 36-47% for that situation where M=Cr, Fe, Co or Ni. In thecase of Mn, yields of 81% are indicated. The relatively low yields notedabove for Cr, Fe, Co or Ni appears to be related to the fact thatcorresponding metal chlorides that are employed to provide such metals(M) in the final (DABD)₂M complex may retain THF in their coordinationsphere, forming initial solvates of the form MCl₂(THF)_(x) (FIG. 1).When lithium and DABD ligand are added to the mixture, differences inthe reaction kinetics make the reduction of these THF solvatescompetitive with the one-electron reduction of the DABD by lithium.Alternatively, the reduced DABD ligand could also act as the directreducing agent given its higher solubility compared to Li metal in thismedium. The undesired reduction of the THF solvate has beenexperimentally confirmed for M=Co. As a result, the one-step protocolwhereby DABD is exposed to THF, CoCl₂ and lithium leads to the formationof insoluble and darkened by-products (presumably mixtures of cobaltoxides), and relatively low yields of 36-47% when M=Cr, Fe, Co or Ni.

The present disclosure therefore provides what may be described as a twostep procedure for the production of transition metalbis-diazabutadienes. Attention is directed to the scheme illustrated inFIG. 2. In a first step, DABD is treated with a transition metal halide(cobalt chloride as the illustrated example) in THF solvent at refluxfor approximately 12 hours. The halide portion may be a chlorine,bromine or iodine atom.

As illustrated, the DABD may include R₁-group substitution on theindicated nitrogen atom where R₁ may by a C₁-C₁₂ alkyl group, amine or aC₆-C₁₈ aryl group. R₂-group substitution on the indicated carbon atomsof the DABD may include hydrogen, a C₁-C₁₀ alkyl, a C₆-C₁₈ aryl group,amino, C₁-C₁₂ alkylamino or a C₂-C₂₄ dialkylamino. When the DABD ligandis treated with MCl₂ in this fashion, without reducing agent (e.g.lithium) present, the product formed is comprised of a complex of theform (DABD)MCl₂. One particularly preferred DABD-transition metal halidecomplex formed in the first step comprises the reaction of CoCl₂ withN,N′-ditertbutyl-1,4-diazabutadiene in refluxing THF, which has thefollowing structure:

The structure depicted above was confirmed by single crystal X-raycrystallography.

Selected Bond Distances and Angles:

Distances (Å): Co(1)-N(1) 2.0538(12); Co(1)-N(2) 2.0601(12); Co(1)-Cl(2)2.2171(4); Co(1)-Cl(1) 2.2194(4); N(1)-C(1) 1.2726(18); N(2)-C(2)1.2675(19). Angles (°): N(1)-Co(1)-N(2) 81.74(5); N(1)-Co(1)-Cl(2)117.89(4); N(2)-Co(1)-Cl(2) 115.73(3); N(1)-Co(1)-Cl(1) 112.44(4);N(2)-Co(1)-Cl(1) 112.30(3); Cl(2)-Co(1)-Cl(1) 113.145(16).

Accordingly, in the first step herein, THF is removed from thecoordination sphere of the metal, preventing reduction of a THF solvatethat may otherwise lead to the formation of cobalt oxides and otherunidentified by-products. In a second step, additional DABD is added tothe DABD-MCl₂ complex, followed by a two-electron reduction of themixture with a reducing agent. As illustrated, the reducing agent waspreferably sodium metal. However, the reducing agent may include anyGroup I metal such as Li, Na, K, Rb or Cs, an alkaline earth metal suchMg or Ca, main group metals such as Zn or Al, a mercury alloy of a maingroup metal such as Na/Hg, Li/Hg or Al/Hg, or an organometallic reducingagent such as C₈K, Cp₂Co or Cp₂*Co. In addition, the reducing agent mayinclude main group hydrides such as lithium aluminum hydride and sodiumborohydride to effect the indicated two-electron reduction. The finalproduct that is formed comprises the bis-diazabutadiene metal complex((DABD)₂M) wherein the yields are 85% or greater. In particular, yieldsupwards of 90% may be achieved when M=Fe, Co, Ni or Cr. Such yieldsestablish the two-step synthesis as a suitable protocol for industrialscale-up. One preferred (DABD)₂M complex formed herein has the followingstructure:

It may therefore be appreciated that in a general embodiment, thepresent disclosure relates to a method for forming a transition metalbis-diazabutadiene comprising the reaction in a first step, in theabsence of a reducing agent, of a diazabutadiene (DABD) with atransition metal halide and forming a DABD-metal halide complex, whereinthe DABD has the following structure:

wherein R₁ is a C₁-C₁₂ alkyl group, amine or a C₆-C₁₈ aryl group and R₂is hydrogen, a C₁-C₁₀ alkyl, a C₆-C₁₈ aryl group, amino, C₁-C₁₂alkylamino or a C₂-C₂₄ dialkylamino group. The formed DABD-metal halidecomplex has the following structure:

wherein R₁ is a C₁-C₁₂ alkyl group, amine or a C₆-C₁₈ aryl group and R₂is hydrogen, a C₁-C₁₀ alkyl, a C₆-C₁₈ aryl group, amino, C₁-C₁₂alkylamino or a C₂-C₂₄ dialkylamino group, X is Cl, Br or I and M is atransition metal. This is then followed by reacting in a second step theDABD-metal halide complex (DABD)MCl₂ with additional DABD in thepresence of a reducing agent and forming a transition metalbis-diazabutadiene of the following structure:

wherein R₁ is a C₁-C₁₂ alkyl group, amine or a C₆-C₁₈ aryl group and R₂is hydrogen, a C₁-C₁₀ alkyl, a C₆-C₁₈ aryl group, amino, C₁-C₁₂alkylamino or a C₂-C₂₄ dialkylamino group and M is a transition metal.The yield of the transition metal bis-diazabutadiene is at or greaterthan 85%.

Preferably, R₁ in the diazabutadiene ligand comprises a C₁-C₁₂ alkylgroup and R₂ in the diazabutadiene comprises hydrogen. In addition, R₁in the DABD-metal halide complex preferably comprises a C₁-C₁₂ alkylgroup and R₂ in the DABD-metal halide complex preferably compriseshydrogen. R₁ in the transition metal bis-diazabutadiene preferablycomprises a C₁-C₁₂ alkyl group and R₂ in the transition metalbis-diazabutadiene comprises hydrogen.

The transition metal halide may comprise a transition metal that isselected from Cr, Fe, Co or Ni and the halide is selected from Cl, Br orI. In particular, the transition metal halide may be Co based and thehalide is Cl.

The reducing agent may preferably comprise Na, Li, Mg or Al. Sodium isparticularly preferred as it is relatively easier to handle than Li,which generally requires operation under an inert atmosphere of Ar, asLi quickly reacts with most commonly used dinitrogen gas to form Li₃N.

The (DABD)₂M complexes produced herein may be advantageously utilizedfor ALD or CVD of a coating on a substrate. Accordingly, any substrateherein may now be coated by the (DABD)₂M precursor complex examples ofwhich include, but are not limited to, silicon wafers, quartz plates,glass plates, etc. The method includes contacting a substrate with the(DABD)₂M complex prepared herein.

The foregoing description of several methods and embodiments has beenpresented for purposes of illustration. It is not intended to beexhaustive or to limit the claims to the precise steps and/or formsdisclosed, and obviously many modifications and variations are possiblein light of the above teaching. It is intended that the scope of thedisclosure be defined by the claims appended hereto.

The invention claimed is:
 1. A method for forming a transition metalbis-diazabutadiene comprising: reacting in a first step, in the absenceof a reducing agent, a diazabutadiene (DABD) with a transition metalhalide and forming a DABD-metal halide complex, wherein said DABD hasthe following structure:

wherein R₁ is a C₁-C₁₂ alkyl group, amine or a C₆-C₁₈ aryl group and R₂is hydrogen, a C₁-C₁₀ alkyl, a C₆-C₁₈ aryl group, amino, C₁-C₁₂alkylamino or a C₂-C₂₄ dialkylamino group; said formed DABD-metal halidecomplex has the following structure:

wherein R₁ is a C₁-C₁₂ alkyl group, amine or a C₆-C₁₈ aryl group and R₂is hydrogen, a C₁-C₁₀ alkyl, a C₆-C₁₈ aryl group, amino, C₁-C₁₂alkylamino or a C₂-C₂₄ dialkylamino group, X is Cl or Br and M is atransition metal; reacting in a second step said DABD-metal halidecomplex with additional DABD in the presence of a reducing agent andforming a transition metal bis-diazabutadiene of the followingstructure:

wherein R₁ is a C₁-C₁₂ alkyl group, amine or a C₆-C₁₈ aryl group and R₂is hydrogen, a C₁-C₁₀ alkyl, a C₆-C₁₈ aryl group, amino, C₁-C₁₂alkylamino or a C₂-C₂₄ dialkylamino group and M is a transition metal;wherein said yield of the transition metal bis-diazabutadiene is at orgreater than 85%.
 2. The method of claim 1 wherein: R₁ in saiddiazabutadiene comprises a C₁-C₁₂ alkyl group; R₂ in said diazabutadienecomprises hydrogen; R₁ in said DABD-metal halide complex comprises aC₁-C₁₂ alkyl group; R₂ in said DABD-metal halide complex compriseshydrogen; R₁ in said transition metal bis-diazabutadiene comprises aC₁-C₁₂ alkyl group; and R₂ in said transition metal bis-diazabutadienecomprises hydrogen.
 3. The method of claim 1 wherein said transitionmetal halide comprises a transition metal that is selected from Cr, Fe,Co or Ni and said halide is selected from Cl, Br or I.
 4. The method ofclaim 3 wherein said transition metal is Co and said halide is Cl. 5.The method of claim 1 wherein said DABD-metal halide complex comprises:


6. The method of claim 1 wherein said transition metalbis-diazabutadiene comprises the following structure:


7. The method of claim 1 wherein said reducing agent comprises Na, Li,Mg or Al.